The present invention relates to a method and apparatus for measuring the degree of cleanliness of a substrate surface.
In the manufacturing process of microelectronic components, particularly in the assembly operation of integrated circuits, many operations require a cleaning step. However, even the most accurate cleaning method can leave some contamination. Many circumstances require that the cleanliness of a surface be tested and measured to verify that the contamination of the part is contained within acceptable limits. Furthermore, a check on the cleanliness of a surface may be required when a part is moved between processing steps where handling or transportation is required. For example, a cleaning or a check of the degree of cleanliness may be required before electroplating of a part, or before a component is soldered onto a plated pad. An example is the mounting of a chip (device) on a substrate, usually done through soldering. This is called xe2x80x9cfirst level packagingxe2x80x9d. This stage of the process needs to be performed in a xe2x80x9ccleanxe2x80x9d environment to avoid contamination of the parts, before the module is encapsulated, usually with a resin, and the circuits are protected by external agents.
The meaning of xe2x80x9ccleanxe2x80x9d can vary significantly according to the application field considered. In precision cleaning applications, in which the required degree of cleanliness is very high, such as in the manufacture of medical components or electronic products, an accurate assessment of surface cleanliness is needed in order to meet the expected quality parameters.
In the manufacturing of electronic components and products, the contamination of a surface can be caused by a number of different factors. Examples of contamination include: the deposition of small particles; ionic contamination; deposition of chemical compound layers (e.g., oils or fluxes) occurring during the manufacturing steps; and adsorption of organic material (e.g., hydrocarbons or moisture) caused by exposure to the atmosphere. If a degree of cleanliness must be ensured, a reliable method of measurement of such degree is needed.
An accurate cleanliness assessment also helps in protecting the environment against pollution from cleaning agents, by evaluating new cleaning methods, or optimizing the existing cleaning processes.
Methods for measuring the degree of cleanliness can be divided in two categories: a) direct methods; and, b)indirect. Direct methods analyze the surface to be checked to discover whether the contamination of the surface exceeds a predetermined threshold. These methods are either dependent on human discretionary power, such as a magnified visual inspection, or require sophisticated and very expensive equipment. Indirect methods are based on the analysis of a very powerful solvent after it has been used to extract the contaminants from a specimen surface.
It should be immediately evident that the above described techniques are very labourious and, in the case of some direct methods, are not completely reliable, because of human intervention. Furthermore, the interruption of the mechanical handling of the modules for the manual checking and refinement, leaves open the eventuality of contamination during the waiting times and the moving of the modules. None of the methods mentioned above are useful to detect the contamination of organic adsorbed layers.
For the above reasons, a more accurate and reliable method would be highly desirable, particularly for the detection of organic contamination of the type described above. It is an object of the present invention to provide a technique which overcomes the above drawbacks.
An object of the present invention is to provide a method for measuring the degree of cleanliness on a substrate surface.
Another object of the present invention is to provide a method for measuring organic contamination on the surface of an inorganic substrate.
Another object of the present invention is to provide an apparatus to determine the degree of cleanliness of a substrate surface by applying a probe to a substrate with a compressive force and measuring the tensile force needed to separate the probe from the substrate surface.
A further object of the present invention is to provide a method of determining the degree of cleanliness of a substrate surface by providing a ratio between the tension force Fw and the pressure force Fi of contacting a substrate surface with a probe and comparing this ratio with a value for a clean surface.
According to one aspect of the present invention, there is provided a method for revealing and estimating contamination on a substrate surface comprising the steps of: bringing a probe in contact with a substrate surface; applying a compression force Fi between the probe and the substrate surface; separating the probe and the substrate surface; measuring the tensile force Fw which opposes the separation; and, comparing the tensile force measured with an expected value for a clean surface.
Further, according to another aspect of the invention, there is provided an apparatus for revealing contamination on a substrate surface and measuring the cleanliness of a substrate surface, comprising: a probe; a system for bringing said probe in contact with the substrate surface; a system for applying a compression force Fi between the probe and the surface; a system for separating the probe and the substrate surface; and, a system for measuring the tensile force Fw required to separate the probe and the substrate surface.
Further, according to yet another aspect of the invention, there is provided an apparatus for revealing contamination on a substrate surface and measuring the cleanliness of the substrate surface comprising: a first member; a substrate having a first surface and second bottom surface, the second bottom surface positioned on the first member; a second member; a probe positioned on said second member; a system for bringing together the substrate first surface and the probe and applying a compressive force; a system for applying a tensile force to separate the substrate first surface and the probe; a system for measuring the compressive force and the tensile force; and, control a system for controlling movement by the probe and the substrate.